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采用焊接热模拟技术和电化学测试技术,研究了Q315NS钢焊接热影响区组织转变规律及焊接热循环对其腐蚀行为的影响。结果表明,Q315NS钢母材、细晶区和混晶区微观组织均由铁素体和珠光体组成,粗晶区主要由粗大的粒状贝氏体组成。在质量分数为50%的H2SO4溶液中,母材和热影响区的等效电路中均包含一个电荷转移电阻和一个由双电层产生的常相位角元件,且均产生了钝化行为。母材和混晶区的电荷转移电阻最大,腐蚀电流密度最小,耐腐蚀性能最好;粗晶区电荷转移电阻最小,腐蚀电流密度最大,耐腐蚀性能最差。腐蚀72 h后,母材、细晶区和混晶区表面生成的腐蚀产物均呈多孔状结构,而粗晶区表面生成的腐蚀产物为短棒状结构。2种结构的腐蚀产物均主要为Fe的硫酸盐,并含有Cu、Sb的氧化物及少量Si。
The influence of welding heat cycle and its microstructure on the corrosion behavior of Q315NS steel was studied by using welding heat simulation and electrochemical testing techniques. The results show that the microstructure of Q315NS steel base metal, fine grain region and mixed grain region are composed of ferrite and pearlite. The coarse grain region is mainly composed of coarse granular bainite. In the 50% H2SO4 solution, the equivalent circuit of the base metal and the heat affected zone contains a charge transfer resistance and a normal phase angle element produced by the electric double layer, both of which produce passivation behavior. The charge transfer resistance of the base metal and the mixed crystal region is the largest, the corrosion current density is the smallest, and the corrosion resistance is the best. The charge transfer resistance of the coarse grain region is the smallest, the corrosion current density is the largest, and the corrosion resistance is the worst. After 72 h of corrosion, the corrosion products produced on the surface of base metal, fine grain and mixed grain all showed porous structure, while the corrosion products formed on the surface of coarse grain were short rod-like structure. The corrosion products of the two structures are mainly sulfates of Fe, and contain oxides of Cu and Sb and a small amount of Si.